It has been estimated that the repairs and down time caused by oil-related engine or other machine failures represent about 30–50% of the operation cost in Australian mining industry. In the economies of developed countries the damage from machine and engine wear represents about 6% of the gross national product. Thus, the development of effective techniques for the reliable prognosis of wear and maintaining the effectiveness of working lubrication oils is of substantial interest. Current diagnostic tests based on Scheduled Oil Sampling can not promptly detect a rapidly progressing component failure or a sudden ingestion of oil contaminants.
Furthermore, in many situations the timing of any oil change is associated with the measured use of the vehicle or machine using the oil rather than the actual condition of the oil. Ideally it would be desirable to monitor the condition of the oil so that information can be obtained about deterioration or contamination in the oil before any catastrophic failure of the machine or machine components can take place.
Different methods have been adopted for monitoring the condition of oil. For example, the specification of U.S. Pat. No. 4,831,362 discloses an apparatus for detecting ferromagnetic particles in lubricating oil. The apparatus consists of two windings inductively coupled via the lubricating oil. A permanent magnet located behind a sensor winding generates a magnetic flux which attracts ferromagnetic particles giving rise to pulses in the sensor winding.
U.S. Pat. No. 5,262,732 describes a system which utilises both a permanent magnet and electro magnet to simultaneously impose their magnetic fields upon the lubricating oil so as to attract ferromagnetic particles in the oil.
U.S. Pat. No. 6,204,656 discloses an array of sensors in conjunction with a magnetic field intensity gradient to obtain a particulate distribution of ferrous particles across the array. Unfortunately, the systems of both of these patents are sensitive to mechanical vibration commonly encountered in moving machines. Furthermore, only limited information can be obtained about degradation of the oil which is being monitored.
Other systems have also been devised for monitoring oil contamination, such as those that measure dielectric constant. However, there is no system which is currently able to monitor a range of oil contaminants and which may be applicable to analysis and monitoring of other fluids.